Lu Bu was planning to mobilize troops, not already on the march, so this naturally was not a report from the northern front.
In truth, this letter had been sent by Chen Deng to Liu Bei. To explain the matter, one had to begin with the situation in Xuzhou.
After the campaign against Yuan Shu last year, Lu Bu and Liu Bei had formed an alliance to resist Cao Cao together.
Following this alliance, Lu Bu received a great deal of money and naturally began recruiting troops and buying horses, expanding his own strength.
By the end of last year, the Mi Clan had begun selling salt throughout Xuzhou using the salt-making method provided by Qin Tian.
Lu Bu received his share of the profits, and the two sides grew ever closer.
Seeing Liu Bei developing southward and Old Cao expanding westward, Lu Bu heeded Qin Song's advice and prepared to head north into Qingzhou, first destroying Zang Ba.
In the Romance, Zang Ba appeared from the outset as one of Lu Bu's Eight Elite Generals, no more than a minor lackey.
But the real Zang Ba was also a hero in his own right, highly skilled in warfare.
Faced with Lu Bu's fierce assault, he personally held the city in defense and battled Lu Bu for two months, forcibly blocking Lu Bu within Langya Kingdom.
Seeing how hard Zang Ba was to crack, Lu Bu had no choice but to lead his troops back to Xiapi.
At that time, Liu Bei was competing with Cao Cao for Chen State. Seeing this, Chen Gong urged Lu Bu to send troops west and seize Pei Commandery while the opportunity was there.
Lu Bu watched Liu Bei gradually grow stronger and naturally felt envious. But remembering their current alliance, as well as